Recently, the horizontal type rotary compressor has been increasingly employed in various types of equipment and therefore, the actual demand for the compressor has been drastically increasing.
The horizontal arrangement of such rotary compressor begets such advantages as saving of installation space, the decrease of vibrations and noises, etc, but requires a separate oil feeding means in order to supply lubricating oil to the sliding portion of a rotating shaft while the level of lubricating oil surface remains low enough to prevent the horizontally positioned rotor portion of a motor from being submerged in the oil. The oil feeding means of conventional rotary compressors may be divided into, for example, the coiled spring pump type as schematically shown in FIG. 5, the fluid diode type as shown in FIG. 6 and the pressure difference type as shown FIG. 7. First, the coiled spring pump type shown in FIG. 5, and as cited in U.S. Pat. No. 4,626,180 as prior art, has a curved oil feeding pipe which is immersed in oil stored in the lower part of a casing. The oil feeding pipe is provided therein with a coiled spring which rotates with a crankshaft. The oil is transferred to the end portion of the crankshaft which is closer to the coiled spring through the leads of the coiled spring. Secondly, the fluid diode type shown in FIG. 6, as disclosed in U.S. Pat. Nos. 4,543,046, 4,544,338 and 4,626,180, includes an oil feeding hole defined inside the shaft provided with oil grooves on the peripheral surface thereof, a fluid diode type oil feeding pump activated by the shaft and a pipe interconnecting the said pump with the said oil feeding hole. However, the oil feeding means adopting the fluid diode method and the coiled spring pump method has certain disadvantages. The configuration thereof is complicated, due to the inclusion of various parts, and the volume of the compressor unit as well as the production cost is increased. Consequently, the possibility of malfunction of the compressor becomes higher and also the life span thereof is shorter. Lastly, the pressure difference type device shown in FIG. 7 and as disclosed in Japanese laid-open patent publication No. 62-58086, comprises, in a casing, an annular space (5) formed between a journal-bearing and a grooved shaft(2), an oil passage(1b) the lower end of which is extended below the oil surface and the higher end of which communicates with the said annular space(5). The annular space(5), the oil passage(1b) and the groove(2a) on the shaft form a sealed space isolated from inner space of the casing. Upon the operation of the compressor unit, the oil stored in the lower part of the casing can be supplied to the sliding portion of the shaft via the sealed space due to the pressure difference between the pressure within the casing and the pressure in the said sealed space. Although the configuration of the pressure difference type oil feeding means is simpler than those of the aforesaid other types, the supply of the oil by this oil feeding means is delayed and the oil feeding to the partial sliding portion where the oil supply groove is not formed is dissatisfactory. Further, the pressure difference type device sometimes malfunctions because the oil cannot be delivered up to the said sliding portion since the pressure difference required to raise the oil cannot be attained within the compressor. The oil feeding means utilizing pressure difference will be described in more detail. A spiral oil groove(2a) is formed only on the inner part of the sliding portion of the shaft(2) so that the said sealed space comprising the oil passage(1b), the annular space(5) and the groove(2a) can be isolated from the other space within the casing(4). Therefore, the pressure in the sealed space can be affected via the lubricant(9) only by the increased pressure within the casing(4) upon the operation of the compressor. Thus, when the compressor starts, via the oil flow passage(5) the lubricant(9) is forcibly delivered by the increased pressure within the casing(4) up to the annular space(5) and to the sliding portion between the shaft(2) and the journal bearing(1b) maintaining the same pressure as before the start of the compressor. Since the sealed space has been occupied by the refrigerant gas, the refrigerant gas is compressed to a certain pressure, which hinders the lubricant from flowing into the said sealed space. Therefore, a larger pressure difference is required to make the lubricant surely reach the sliding portion of the shaft. For these reasons, the supply of the lubricant to the said sliding portion may be delayed and, furthermore, the supply of the lubricant to the said sliding portion may not be accomplished because the required pressure difference is not formed. On the other hand, since the oil groove is formed on the inner part of the sliding portion of the shaft, the lubricant cannot be delivered sufficiently to the outer sliding portion where the oil groove is not formed. As a result, the sliding portion of the shaft is easily abraded and, therefore, the life span of the compressor is remarkably shortened. In order to overcome this problem, anti-compression agents are sometimes added to the lubricant, but these merely result in the increase of the production cost of the compressor. In addition, as mentioned above, since the oil groove is formed partially on the sliding portion of the shaft to keep the said closed space gas-tight, if micro-chips or other hard dirts are delivered with the lubricant into the said sliding portion, such foreign objects will intervene in the sliding portion between the journal-bearing and the shaft. Since they cannot escape from the said sliding portion, the result will be the mechanical locking of the shaft and journal bearing resulting is the fatal malfunction of the compressor and/or the undesirable formation on deep scratches on the sliding portion. Consequently, in order to prevent those problems, the perfect cleaning of parts before assembling of the compressor as well as the precise control of the foreign materials in the lubricant is required, which results in the increase of the production cost of the compressor.